Intravascular device positioning, including navigating the device to its target location and deploying the device at the target location is generally performed under imaging by one of several imaging modalities. A modality commonly used for this purpose is X-ray angiography. The target location for positioning the device is usually seen well when contrast material is injected into the vessel, making the vessels clearly distinguishable. However, each contrast injection exposes the target for only a few seconds, and repeated injections are considered damaging as contrast material is harmful for the kidneys, and excessive radiation is unsafe for the whole body. Moreover, on some procedures and for some kinds of therapeutic devices, the contrast material hides the therapeutic device, making assessment of the device location and thus navigating the device to the required location difficult.
The positioning task is especially difficult for moving organs. For example the heart is subject to its own cyclic motion, breathing, and patient or bed movements. These movements make positioning even more difficult.
Several positioning solutions have been introduced for positioning a device. Some systems, such as International Patent Application published as US2006/0058647, use dedicated equipment based on optical, electromagnetic, or ultrasonic principles for localizing the device. These methods, when applicable, require a complicated calibration procedure. An added modality considerably increases the overall complexity and cost of the procedure. International patent application publication WO 06/103644 discloses a method for registration between an image showing a device using X-Ray and a reference image showing the vessel and the target location, and presenting the device on this reference image. This method is computationally expensive and may provide inaccurate results under conditions of complex motion of the organ. This method is limited since high level of similarity is required between positioning images taken during the therapeutic stage showing the device, and images taken during the reference state showing the organ.
International patent application publication WO 05/020148 discloses a method for overcoming the motion artifact by using data banks containing static vascular maps relating to different phases of the cardiac/respiratory cycles. The positioning image is associated with the corresponding image in the bank by ECG and measured respiration phase. The suggested method requires additional equipment, is not accurate, and does not relate to all the motions, including for example patient movements.
International patent application titled PCT/IL2006/000793 discloses a method for positioning a device in a tubular organ using a guidewire with special markings. Navigation of the device to the target location is carried out using the relation between the markings and the target, the relation extracted by analyzing a reference sequence of images. In addition to the necessity to use a special guidewire, the approach suffers from a number of additional drawbacks. Additional markers on the guidewire make the task of detecting and tracking the device markers much harder. In addition, the method assumes that the guidewire is fixed relatively to the artery throughout the heart motion cycle, which is not always valid. In such cases. shifts of the guidewire inside the vessel introduce inaccuracies.
Thus there is a need in the art for a method for guiding a therapeutic device to an invisible target location in a moving organ. The method should be accurate under typical motions, and reduce the navigation time of the device to the location, as yell as the need for contrast injections.